Human lung cancer A549 and SPCA-1 cell lines were irradiated by X-rays at the absorbed doses of 1, 3, 5 and 8 Gy, respectively, generated by a linear accelerator (with the source skin distance of 100 cm and dose rate of 200 cGy•min−1). The cell molecular samples were subtracted at 6 h, 12 h, and 24 h after 5 Gy ionizing irradiation. For the study of X-rays and cisplatin combination treatment, cells were divided into radiation group (5 Gy X-rays), cisplatin group (20 µmol•L−1 cisplatin), and combination group (5 Gy X-rays + 20 µmol•L−1 cisplatin). Untreated cells were classified as control group. The relative levels of BTG3 mRNA and protein expression in cells were detected by semi-quantitative RT-PCR and Western blot analysis with quantitation of the mRNA/protein bands by densitometry. The expression level of BTG3 mRNA and protein significantly increased with the dose climbed after radiation exposure of human lung cancer A549 and SPCA-1 cell lines (t=5.25−15.75, p<0.05). The expression level in cancer cells significantly increased 4 h after radiation exposure and kept increasing until 24 h later (t=7.52−11.18, p<0.05). Compared with that of the radiation and/or cisplatin treatment alone, more significant increase of BTG3 expression was identified after the combination treatment of X-rays and cisplatin (t=7.02−15.86, p<0.05). Ionizing radiation could up-regulate the expression of BTG3 in human lung cancer cells in both mRNA and protein levels. BTG3 gene may be targeted as a molecular for ionizing radiation and cisplatin treatment in lung cancer.Cited